Thursday, in between the cheese ball appetizers and the pumpkin pie desserts, most of us will indulge in something proven to have powerful health benefits.

No, it’s not that extra serving of stuffing. It’s the expression of gratitude — the simple act of thanking God, thanking others or just counting your blessings. Saying thanks, it turns out, isn’t just pious or polite. It’s good for you.

But there’s a catch: You have to do it even when the calendar does not say “Thanksgiving.”

“It doesn’t really work if you do it only once a year,” says Sonja Lyubomirsky, professor of psychology at the University of California-Riverside.

Practicing gratitude is like exercising, says Robert Emmons, professor of psychology at the University of California-Davis: Use it, and you won’t lose it, even when times are tough, as they are for many folks right now.

Lyubomirsky and Emmons are among researchers who have studied the power of gratitude and learned, for example, that:

• People with high blood pressure not only lower their blood pressure, but feel less hostile and are more likely quit smoking and lose weight when they practice gratitude. In one study, patients just called a research hotline once a week to report on the things that made them grateful.

• People who care for relatives with Alzheimer’s disease feel less stress and depression when they keep daily gratitude journals, listing the positive things in their lives.

• Those who maintain a thankful attitude through life appear to have lower risks of several disorders, including depression, phobias, bulimia and alcoholism.

• Most people can lift their mood simply by writing a letter of thanks to someone. Hand-deliver the letter, and the boost in happiness can last weeks or months.

Practicing gratitude in these systematic ways changes people by changing brains that “are wired for negativity, for noticing gaps and omissions,” Emmons says. “When you express a feeling, you amplify it. When you express anger, you get angrier; when you express gratitude, you become more grateful.”

And grateful people, he says, don’t focus so much on pain and problems. They also are quicker to realize they have friends, families and communities to assist them in times of need. They see how they can help others in distress as well, he says.

After 9/11, many people reported increased feelings of gratitude, says Chris Peterson, a professor of psychology at the University of Michigan.

It’s too soon for studies on the influence of the nation’s financial meltdown, but Peterson says he hears a lot of people counting their blessing these days. “There are people who say ‘It could be worse, and I’m glad I have my health.’ “

Gratitude won’t get those people new jobs or replenish their retirement accounts, but it could give them the energy to tackle their challenges, Peterson says: